Meal-contingent intestinal lymph sampling from awake, unrestrained rats

Standard procedures for intestinal lymph collection involve continuous, quantitative drainage of the lymph fluid in anesthetized or restrained animals that are often euthanized within 48 h. We here describe a novel technique for the nonocclusive cannulation of the major intestinal lymph duct in rats that allows for repetitive in vivo sampling of intestinal lymph from unrestrained, awake, and ad libitum-fed animals. The distinctive feature of this novel technique is that a 5- to 7-mm long piece of Vialon tubing (OD/ID: 0.8/0.7 mm) with a small hole in its wall is first implanted into the major intestinal lymph duct for stabilization. The tapered tip (OD: ≈0.1 mm) of the catheter is then inserted into the hole of the tubing and fixed in place with a polyamid suture and a drop of tissue glue. In our hands, catheters implanted this way remain patent for up to 6 wk after surgery. In an initial experiment we collected lymph from six adult rats before (0) and 15, 30, 45, 60, 75, 90, 120, and 180 min (120 μl, each) after the onset of isocaloric (12.5 kcal) low-fat (LF) or high-fat (HF) test meals and measured active glucagon-like peptide-1 (GLP-1). Intestinal lymphatic GLP-1 concentration increased (P < 0.05) from ≈4 pmol/l (0 min) to a peak of 33 ± 6 (means ± SE) or 22 ± 4 pmol/l at 15 (HF) or 30 min (LF) after meal onset and gradually returned to baseline levels by 180 min. With this new technique fewer animals are required to generate physiologically relevant data for various aspects of gastrointestinal physiology that involve the lymphatic system. Furthermore, the advantage of this system is that the animal can act as its own control when the effect of different experimental protocols is tested.     

Functional MRI in awake unrestrained dogs

Because of dogs' prolonged evolution with humans, many of the canine cognitive skills are thought to represent a selection of traits that make dogs particularly sensitive to human cues. But how does the dog mind actually work? To develop a methodology to answer this question, we trained two dogs to remain motionless for the duration required to collect quality fMRI images by using positive reinforcement without sedation or physical restraints. The task was designed to determine which brain circuits differentially respond to human hand signals denoting the presence or absence of a food reward. Head motion within trials was less than 1 mm. Consistent with prior reinforcement learning literature, we observed caudate activation in both dogs in response to the hand signal denoting reward versus no-reward.     

Chronic polyelectromyography in awake, unrestrained animals.

A procedure is described for making an implantable electrode array for recording EMG activity in muscles of awake, unrestrained animals (rats and cats) at rest, during rhythmic activity and in response to various reflexogenic stimuli. The electrode array consists of a percutaneous connector (covered with Dow-Corning Silastic Medical Adhesive), steel wire spiral leads contained in silicone tubing and silicone plate probes with platinum electrodes. These plate probes can be fixed either to the bone underneath the muscle, slipped under the fascia, or fixed between muscles. EMG records are presented of postural activity and ambulation in rats, mastication in cats and unilateral and bilateral spinal and supraspinal reflex responses in rat hind limb muscles up to 6 months after implantation. The advantages (and drawbacks) of this technique and its possible uses in neurophysiology are enumerated in the discussion.     

Moderate hypothermia induces a preferential increase in pancreatic islet blood flow in anesthetized rats

The aim of the study was to characterize the effects of induced moderate hypothermia on splanchnic blood flow, with particular reference to that of the pancreas and the islets of Langerhans. We also investigated how interference with the autonomic nervous system at different levels influenced the blood perfusion during hypothermia. For this purpose, hypothermia (body temperature of 28 degrees C) was induced by external cooling, whereas normothermic (37.5 degrees C) anesthetized Sprague-Dawley rats were used as controls. Some rats were pretreated with either propranolol, yohimbine, atropine, hexamethonium, or a bilateral abdominal vagotomy. Our findings suggest that moderate hypothermia elicits complex, organ-specific circulatory changes, with increased perfusion noted in the pylorus, as well as the whole pancreas and the pancreatic islets. The pancreatic islets maintain their high blood perfusion through mechanisms involving both sympathetic and parasympathetic mediators, whereas the increased pyloric blood flow is mediated through parasympathetic mechanisms. Renal blood flow was decreased, and this can be prevented by ganglionic blockade and is also influenced by beta-adrenoceptors.     

神经节苷脂与头部贴敷式亚低温联合治疗对新生鼠缺氧缺血性脑损伤的影响

目的:研究神经节苷脂与头部贴敷式亚低温联合治疗新生鼠缺氧缺血性脑损伤时脑组织内一氧化氮(NO)和(MDA)含量的变化,为新生儿缺氧缺血性脑病的治疗提供理论依据.方法:将88只WISTAR新生鼠随机分为四组,神经节苷脂治疗组(IG)、头部贴敷式亚低温治疗组(IH)、联合治疗组(IB)以及对照组(CN).结果:CN组NO和MDA的含量明显升高,IG、IH以及IB组NO和MDA均明显下降.结论:神经节苷脂和亚低温通过降低NO和MDA的含量保护缺氧缺血神经元,二者联合效果更好.     

Effect of mild hypothermia on blood brain barrier disruption induced by oleic acid in rats

The blood-brain barrier (BBB) is essential for the normal function of the central nervous system. The pathological conditions induced by brain diseases including cerebral ischemia result in the alteration of BBB integrity. This alteration of BBB is relieved by mild hypothermia that has been regarded as an effective therapy for brain injury. Experimental fat embolism by intra-arterial administration of fatty acid induces reversible dysfunction of BBB and is considered as a beneficial method for the research on BBB disruption. However, the implication of hypothermia on the fatty acid-induced BBB disruption is not clear yet. In this study, we aim to investigate the effect of mild hypothermia on BBB disruption by comparing the changes of brain inflammation, free radical production, and matrix metalloproteinases (MMPs) caused by cerebral fatty acid infusion between normothermic (37°C) and hypothermic (33°C) groups. Oleic acid infusion into the carotid artery induced the increase of BBB permeability, which was inhibited by mild hypothermia. Neutrophils were infiltrated and intercellular adhesion molecule-1 (ICAM-1) expression was increased in the vascular structures in the affected brain tissue of normothermic rats at 24 hrs following oleic acid administration. Inducible nitric oxide synthase (iNOS) and nitro-tyrosine immunoreactivities were also observed in the normothermic group. The expression of matrix metalloproteinase (MMP)-2, 3, and 13 were upregulated predominantly in the oleic acid-treated brain of the normothermic rats. In mild hypothermic condition, neutrophil infiltration and ICAM-1 expression were attenuated, whereas the inductions of iNOS, nitrotyrosine and MMPs except MMP3 were not affected. Therefore, we suggest that mild hypothermia contributes to the protective effect on oleic acid-induced BBB damage via reducing neutrophil infiltration and brain inflammation.     

The anxyolytic effect of mild hypobaric hypoxia in a model of post-traumatic stress disorder in rats

The impact of mild hypobaric hypoxia on the development of anxiety-like state in rats in experimentally simulated human post-traumatic stress disorder was studied. Three-trial exposure to mild hypobaric hypoxia (360 mm Hg for 2 hours daily, for 3 days) in preconditioning or post-conditioning mode performed, respectively, before or after exposure to severe traumatic stress in the "stress-restress" model produced a significant anxiolytic effect on the rat open-field and plus-maze behavior. Anxiolytic effect of modem antidepressant Paxil (20 mg/kg daily, for 3 days) was weaker. This drug produced side-effects on particular behavioral characteristics in the open field. The conclusion was made on the efficacy of mild hypobaric hypoxia and the possibility of its implementation as a medication-free tool for prophylaxis and correction of post-traumatic stress disorder.     

Transient mild hypothermia differentially alters mitotic activity in normal and post-ischemic hippocampal slices from neonatal rats

The purpose of this study was to determine if mild hypothermia alters mitotic activity in normal and post-ischemic hippocampal slices. (1) Normothermic oxygen–glucose deprivation (OGD 60 min) increased mitotic activity in the hippocampus up to 4d post-OGD. (2) Mild hypothermia (33 °C for 24 h) initiated after OGD stress reduced mitotic activity compared to normothermic controls up to 8 d post-OGD. (3) Mild hypothermia stimulated mitotic activity in normal (no OGD stress) hippocampus up to 24 h post-hypothermia. In conclusion, mild transient hypothermia can increase or decrease mitotic activity depending upon the experimental condition of the hippocampal slices when hypothermia is induced.     

Ventilation and acid-base balance in awake dogs exposed to heat and CO2

Some awake quiet dogs pant at cool ambient temperature (Ta) and some do not pant even when acutely exposed to heat. The purpose of the study was to determine whether this puzzling variability in respiratory behavior diminished during prolonged heat. The contributions of thermal and CO2 drives to respiratory adaptations were also examined. Five awake dogs acclimated to 20 degrees C were studied before and 2 and 48 h following exposure to 30-31 degrees C. Rectal temperature did not change; the important thermal stimulus, even at 48 h, appeared to be the increase in peripheral temperature. Variability between nonpanting and panting persisted over 48 h. On the average, ventilation (VE) doubled during heat, largely due to increased dead space ventilation. Nonpanting dogs at cool Ta decreased the threshold of the ventilatory response to CO2. A panting dog at cool Ta changed its slope of the ventilatory response from negative to positive. During hypercapnia in acute heat, ventilatory pattern changed so that frequency increased and tidal volume decreased for a given VE. By 48 h of heat, the ventilatory response to CO2 returned to control in only two dogs, but the ventilatory pattern during hypercapnia returned to control in four dogs. Since thermal stimuli remained unchanged at 48 h, adaptations of respiratory control may have been related to progressive adjustments of strong ions and acid-base balance.     

Noninvasive technique for the repeated sampling of salivary free cortisol in awake,unrestrained squirrel monkeys

The use of noninvasive measures of hypothalamic-pituitary-adrenal (HPA) axis function is of growing interest among preclinical and clinical investigators. This report describes a method for the repeated assessment of salivary free cortisol in awake, unrestrained squirrel monkeys (Saimiri sciureus) based on a saliva sampling technique previously developed for rhesus monkeys. Individually housed adult male squirrel monkeys were trained to chew on dental rope attached to a pole, from which saliva was extracted by centrifugation and analyzed for cortisol by radioimmunoassay (RIA). Eight of nine monkeys readily acquired the task, reliably providing adequate saliva samples for the assay. Salivary free cortisol levels were examined in these subjects under basal conditions and in response to two types of neuroendocrine challenge. Levels of salivary free cortisol showed relatively low intra- and interindividual variability, with mean individual morning levels ranging between 17.1 and 37.9 microg/dl. Squirrel monkeys demonstrated a consistent daily rhythm in salivary free cortisol ranging from a high of 27.4 +/- 5.2 microg/dl (mean +/- SEM) at 12 P.M. to a low of 7.5 +/- 1.6 microg/dl at 6 P.M. Intravenous (IV) challenges with 1 microg/kg ACTH, or 10 and 50 microg/kg CRF resulted in significant increases in salivary free cortisol. The described sampling technique provides a reliable and sensitive means for repeated measurement of HPA activity in unrestrained, awake squirrel monkeys. In addition, our findings illustrate several features of HPA system rhythmicity and reactivity using salivary cortisol instead of blood plasma or serum.     

Angiotensin II-induced hypothermia in rats

Systemic administration of angiotensin II (ANG II) (200 micrograms/kg sc) to the rat induced a hypothermic response that was characterized within 12 min by a reduction in the rate of O2 consumption, vasodilation of the tail, and a 1.3 degrees C fall in colonic temperature. Administration of ANG II in doses ranging from 10 to 200 micrograms/kg resulted in a decrease in colonic and an increase in tail skin temperature. Angiotensin I (ANG I) (200 micrograms/kg sc) induced a similar hypothermic response which was abolished by pretreatment with the ANG I-converting enzyme inhibitor, captopril (35 mg/kg ip). The interaction of ANG II with cholinergic and adrenergic pathways was evaluated to determine possible mechanisms. Treatment with ANG II (200 micrograms/kg sc) and propranolol, a beta-adrenoceptor antagonist (6 mg/kg ip), resulted in a greater depression of colonic temperature (Tco) than was observed with ANG II alone but did not affect the increase in tail skin temperature (Tsk) accompanying administration of ANG II. When ANG II was administered in combination with the beta-adrenergic agonist, isoproterenol (50 micrograms/kg ip), Tco remained at control levels, whereas an enhancement of the ANG II-induced increase in Tsk occurred. Administration of ANG II in combination with atropine sulfate (6 mg/kg ip), a muscarinic receptor antagonist which crosses the blood-brain barrier, significantly reduced the extent of the fall in Tco without affecting the increase in Tsk. The combined treatment of ANG II and the quaternary analogue, atropine methyl nitrate (3.25 mg/kg ip), which does not cross the blood-brain barrier, failed to affect the hypothermic responses to ANG II. These results suggest that the hypothermic responses to ANG II may be mediated through a central cholinergic pathway and possibly influenced by an adrenergic component. The inability of both adrenergic and cholinergic blockers to affect the vasodilatory response of the tail of the rat to administration of ANG II suggests that the mechanisms subserving heat production can be blocked independently of those subserving heat loss.     

Acute spinal cord injury induces genetic damage in multiple organs of rats

Spinal cord injury (SCI) is a devastating condition with important functional and psychological consequences. However, the underlying mechanisms by which these alterations occur are still not fully understood. The aim of this study was to analyze genomic instability in multiple organs in the acute phase of SCI by means of single cell gel (comet) assay. Rats were randomly distributed into two groups (n = 5): a SHAM and a SCI group killed 24 h after cord transection surgery. The results pointed out genetic damage in blood cells as depicted by the tail moment results. DNA breakage was also detected in liver and kidney cells after SCI. Taken together, our results suggest that SCI induces genomic damage in multiple organs of Wistar rats.